(1) Field of the Invention
The present invention relates to an adsorbent for the recovery of bromine and a process for recovering bromine from a bromine-containing aqueous solution or gas by using this adsorbent.
(2) Description of the Related Art
As the main industrial material for bromine, sea water, concentrated sea water, bittern, and natural salt water are used. Bromine is always present in these materials, in the form of a dilute solution. The industrial process for the preparation of bromine comprises oxidizing a bromine ion contained in an aqueous solution as mentioned above with an oxidizing agent such as chlorine to form free bromine, and separating and collecting the free bromine from the aqueous solution.
As means for separating and collecting free bromine from the aqueous solution, there have been industrially adopted (a) a method in which free bromine is expelled by air and (b) a method in which the aqueous solution is directly subjected to steam distillation.
However, these methods have advantages and disadvantages. For example, the former method of expelling bromine by air has a problem in that special means is necessary for separating bromine from the air because bromine is taken out in the form of a gaseous mixture with air, and in this method, a chemical such as caustic soda, sodium bromide or sulfurous acid gas is used as the separating means to collect bromine alone. Therefore, an additional step is necessary for recovering bromine in the free form. Accordingly, this method is regarded as a concentrating method rather than a recovering method. In the latter direct steam distillation method, a very large quantity of steam is necessary for the recovery of bromine. In these methods, as seen from the foregoing description, large quantities for a chemical and energy must be used and the costs of the chemical and energy are a large part of the manufacturing cost.
As another bromine-recovering means, a method is known in which free bromine is adsorbed in a strongly basic anion exchange resin. According to this method, an aqueous solution containing free bromine is placed in contact with a strongly basic anion exchange resin to adsorb bromine in the resin, and the bromine is directly recovered by using a chemical having a high reactivity with bromine such as a mixed aqueous solution of caustic soda and sodium sulfite (Japanese Patent No. 212,506) or an aqueous solution of sodium sulfite (U.S. Pat. No. 3,037,845) or by heating the resin by steam distillation (Japanese Unexamined Patent Publication No. 56-59603 and No. 57-129804). Furthermore, a method is proposed in which a bromine-containing gas is placed in contact with a porous, strongly basic anion exchange resin to adsorb bromine in the resin, and the bromine-adsorbed resin is heated by blowing steam into the resin to desorb and recover bromine (Japanese Unexamined Patent Publication No. 55-109201). A strongly basic anion exchange resin can absorb therein free bromine contained in an aqueous solution or gas, but in the method using a chemical for the desorption, an additional step is necessary for recovering free bromine.
The method for desorbing bromine by heating with steam is advantageous in that bromine is directly recovered. However, the strongly basic anion exchange resin generally has unsatisfactory durability characteristics such as oxidation resistance and heat resistance and cannot be regarded as a satisfactory adsorbent which can be used under severe conditions wherein adsorption and desorption operations are repeated on an industrial scale.